Method of controlling the partial blowing of bessemer steel



Sept. 24, 1957 D. w. MURPHY 2,807,537

METHOD OF CONTROLLING THE PARTIAL BLOWING OF BESSEMER STEEL Filed Nov. 1, 1954 3 Sheets-5heet l TIME -|NTENS|TY INVENTOR'" fiori ald W. Mar a/2y Sept. 24, 1957 D. w. MURPHY 2,807,537

METHOD OF CQNTRQLLING THE PARTIAL BLOWING OF BESSEMER STEEL Filed Nov. 1, 1954 3 Sheets-Sheet 2 EFFECT 01- NUMBER TUYERES BLANKED ON'CARBON PLATEAU 0 THEORETICAL VAL JES BASED ON RELATIVEI EFFECTIVE AREAS 0 EXPERIMENTAL Vfi LUES CHART DIVISIONS o 2 4 's a |0 |2 NUMBER TUYERES BLANKED 1N VENTOR Donald W Mar o/2y TTOR EY p 1957 D. w. MURPHY 2,807,537

METHOD OF CONTROLLING THE PARTIAL BLOWING OF BESSEMER STEEL Filed Nov. 1, 1954 5 Sheets-Sheet 3 CARBON VALUES DURING CARBON PLATEAU PERCENT CARBON 0 2O 4O 60 8O I00 PERCENT OF CARBON PLATEAU 1N VENTOR fiona/d WIMurp/zy 0 NEY United States Patent() 2,807537 METHOD OF CONTROLLING'T'HE PARTIAL BLOWING OFTBESSEMERSTEEL' Donald W. 'Murphy, Bethlehem, 1311., assignor toBcthlehem Steel'Company, .a corporation of Pennsylvania Application'November 1,.J1954,-.Sei ialiNo. 466,069

S'Claims. (Cl.175--60) This invention is a method for controlling the partial .blowingiof Bessemer-steel to obtain metal of any -required carbon content.

In standard Bwsemer converter praeticegimmediately after the vessel hasreceived the chargeofmolten' metal,

the air blast is turned on, and-the vessel'is racked' up to vertical position- Theair of theblastis forced upward through the molten mass, and chemicalaction between "the oxygen of the air and' the contents of: the vesselthen begins. The-oxidationtakes place in-successivestages,

1 each of which may be'observed visually. In'the' first stage,

is being-removed. Just before the end of the carbonblow,

in ordinary practice; theflame-begins to drop and becomes less luminous. When the-vessel is turned .downand the "blow is stopped'at this point,-or shortly thereafter,-only very smallamounts'of carbon, e. g.,' 0.1 to-"0. 04percent,'

will remain, and itthenbecomes necessary toaddrecarburizers and deoxidizers to restore' 'the 'desired ca'rbon content.

While the theoretical possibility of blowing -a i heat to approximatelyany carbon content by stopping the blow .at an'intermediate point has'long been understood,- the reactions involved-are -sorapid that: it has been believed that products :'of uniform chemical 'compositiomcould a only be obtained'by blowing to. the dropf thefiame, as. above described, or-until' substantially#all the carbon had "been removed.

In such efforts at timed carbon-control --as have"been made, the blower has attempted to control carbon content by regulating the length of the 'blow from th'e' time the. 50 vessel-is turned up. This practice will result in variations ofvas much aS='0:5-lp61C6Il' PlUS or minus indesired cari bon; whereas the instant inventionpermits Bessemer-blows to be I terminatedatany desired carbon level .cbetween 3 percent and 0.1' percentwithin a range of'plus or minus ;.0.15 '-percent carbon-'or less. This result Of' the 'inVention 1 isespecially valuableim the :so' calledduplex p-ro'ces s, in

which the semi-finished metal is transferred to an open hearthiurnace forihecompletionrof the, process.

One object of this invention, therefore, is to provide a method forcontrolling the partial blowing of a Bessemer I converter: taproducesteehofi any.desire'd carboneontent.

Another tobjectisJo -establish .a: referenceepoint f-rom which the-irate of carbon. eliminationvis linear and a ,pre-

dictable function of time.

Other objects, purposes and advantages will appear hereinafter, in the specification, drawings and claims.

In the annexed three (3) sheets of drawings: a Fig. l is a typical curve of radiant energy emission during the blow of a heat, and showing the carbon plateau; Fig. 2 is a curve showing the effect of the number of 2,807,537 Patented Sept. 24, 1957 ice =tuyeresblanked on the duration of the carbon plateau; "and :Fig. 3-illustrates the linear elimination of carbon at variouspercentages of the carbon-plateau.

I 5 In a typical installation, a photo-electric tube issighted IQ termination of Temperature of: Molten Metal, which filter is adapted to transmitonlyladiationina wavelength rangein which the characteristiczradiation of iron is predominant, more specifically in the ultraviolet range between 0.32 and 0.36 micron, in which range I have found that the radiation intensity is uniformly correlated with the temperature of the bath. This. tube converts the radiant energy into an electric current which ismeasured and permanently recorded as a curve onsa chart by a high speed recorder. A typical curve' is shown in Fig. l, with the more significant pointsiof changeindicated by reference letters. Thus, the blowstarts at point A but the oxidation of carbon does notf'begin until point B is reached. At point C .the carbomblow is fully developed. This reference point C marks the start of the carbon plateau to be hereinafter discussed, and which extends to the'zpointzD. 'ThepointE'marks .the;.end;of' the blow. The ifcarbonplateau is.thezonly.periodz'during the ".blow inrwhichthe'rate of carbon elimination is a=:pre- ":dicta'ble.rfunction oftime or .volumeiof .air) -Asshown .:in Fig. l, the :duration 'of'thercarbon plateau, or the-z distance'from'C to. D, is somewhatrmorethan' six-divisions on the time scale, with each division. representing-approxi- :zmately tone minute of. blowing time, :but the carbon-.pla- -..teau :period will lengthen proportionately. as more "and more .tuyeres of .the particular bottom are blanked out .ibecause'. of weariand breakage. I iSincezthe blastipressure.appliedto aspecific converter -.is.nsually.:a substantially"fixediquantity; the real criterion ."of'.thezlength:of.the.carbon plateau will'then- :be' the ratio of the effective area of the tuyeres innseto'thatof the ,7 total number ofavailable tuyeres. However, as the: exact number oftuyeres .in.use will alwaysjbe knownto the operator, this provides the most convenientindication of relative areas.

The following table (Table I) embodies the results, of observations itaken over 425 heats with regardto 'the minfluenceconlength. of..:carbon..plateau .of theanumber' 'of tuyeres --blanke'd;.on :a converter having 26 available .-.tuyeres: r a

Table I.Influence ofnumber of blanked tuyeres 1 Number heats -:Duyeres Ave: chart :blanked div.

vA9... .6 7; 75 i2 3 3'5 2 .11 $10.0

Fig. "2 represents. the above "data in curvefform. fIThe dotted'curve is calculated from the number of'tuyeres in "use'rla'tive to the total'number available in 'a new bottom and is based on an average carbon plateau duration of six time divisions for new bottoms. The solid curve is drawn from experimental values. For all practical purposes, the two curves coincide until more than six tuyeres are blocked off.

The significance of various particular points on the carbon plateau with respect to the carbon content of the 2,ao7,:ss7

Table Il.--Percent carbon during carbon plateau Percentage Percentage of carbon of carbon plateau These results are plotted as a function of distance along the carbon plateau in Fig. 3. It is to be noted that the elimination of carbon proceeds linearly with. time during the carbon plateau and with remarkable regularity from thebeginning at about 3.0 percent carbon to the end at about 0.1 percent carbon. .The most critical reference point is the beginning of the carbon plateau.

The following tabulation (Table III) summarizes a typical relationship under normal operating blast pressures (in the neighborhood of 20 pounds per square inch) between number of working tuyeres, length of time in carbon blow, and carbon content of blown metal. This table. can be regarded as a working basis for time of turning down the vessel and shutting off the blast in the controlmethod of the present invention.

Table III.Relationship between number of working tuyeres and length of carbon blow for various finishing carbon contents It is important to notethat the instant of full development ofthe carbon blow (point C, Fig. 1) is independent of calibration, since it is a pointon the time scaleof the record. Within rather wide limits metal temperature does not affect the position of this point on the time scale, with the exception of those heats which have reached either too low or much too high a temperature during the preceding silicon blow. Since the filter and instruments used will provide very accurate indication of temperature,

however, such conditions are readily corrected by well known means during the progress of the blow.

Although this invention has been described hereinabove in considerable detail, it is not desired to have it limited to the exact and specific particulars stated, but there may also be used such modifications, substitutes or equivalents thereof as are included within the scope and spirit of the invention or pointed out in the appended claims.

What is claimed is:

1. In a method of controlling a Bessemer converter, the steps including applying blast to a bath of molten metal, measuring and recording the radiant energy emitted by the converter flame during the blow of the heat, taken the start of the carbon plateau on the record of such emission as a reference point, continuing to apply the blast and turning down the vessel and shutting off the blast at a predetermined period of time after the occur rence of said reference point to obtain the desired carbon level in the bath.

2. In a method of controlling a Bessemer converter, the steps including applying blast to the bath, measuring and recording the radiant energy emitted by the flame within a frequency band in which the characteristic radiation frequency of iron is predominant, taking the start of the carbon plateau on the record of such emission as a reference point, continuing to apply the blast for a period of time after the occurrence of the reference point determined by the desired carbon content of the finished metal and then turning down the vessel and shutting off the blast.

3. In a method of controlling a Bessemer converter,

. the steps including applying blast of known characteristics to the bath, measuring and recording the radiant energy emitted from a zone above said bath during the blow, taking the moment when full development of the carbon blow begins as a reference point for the start of the period of linear elimination of carbon, continuing to apply the blast for a period of time after the occurrence of the reference point determined by the amount of the blast and the desired carbon content of the finished metal and turning down the vessel and shutting off the blast when that period of time has elapsed.

4. In a method of controlling the partial blowing of Bessemer steel to any desired carbon content by means of a phototube, the steps including applying air blast to V the bath, recording the radiant energy from the converter flame intercepted by the phototube, taking the beginning of the carbon plateau as a reference point, and turning down the vessel and stopping the blow when the elapsed time after the occurrence of the reference point indicates that the desired carbon content of the metal in the converter has been reached.

5. In a method of controlling the partial blowing of Bessemer steel to any desired carbon content by photoelectric means, the steps including applying air blast to the bath, recording the radiant energy from the converter flame incident upon the photoelectric means, taking the beginning of the carbon plateau as a reference point, and turning down the vessel and stopping the blow when the desired carbon content of the metal in the converter has been reached as determined by reference to said reference point.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,309 Work July 9, 1940 2,354,400 Percy July 25,1944 2,595,792 Jordan May 6, 1952 

1. IN A METHOD OF CONTROLLING A BESSEMER CONVERTER, THE STEPS INCLUDING APPLYING BLAST TO A BATH OF MOLTEN METAL, MEASURING AND RECORDING THE RADIANT ENERGY EMITTED BY THE CONVERTER FLAME DURING THE BLOW OF THE HEAT TAKEN THE START OF THE CARBON PLATEAU ON THE RECORD OF SUCH EMISSION AS A REFERENCE POINT, CONTINUING TO APPLY THE BLAST AND TURNING DOWN THE VESSEL AND SHUTTING OFF THE 